Submitted to: Sheep and Goat Research Journal
Publication Type: Peer reviewed journal
Publication Acceptance Date: 7/1/2002
Publication Date: 7/25/2002
Citation: Leymaster, K.A. 2002. Fundamental aspects of crossbreeding of sheep: Use of breed diversity to improve efficiency of meat production. Sheep and Goat Research Journal. 17(3):50-59. Interpretive Summary: Breed diversity is an invaluable resource of the sheep industry. Crossbreeding systems use breed diversity to significantly increase productivity relative to purebred flocks. Crossbreeding systems vary in managerial complexity and use of beneficial effects due to crossbred ewes and lambs. Efficiency of meat production is maximized in terminal crossbreeding systems by use of specialized sire breeds to complement characteristics of crossbred ewes. This manuscript addresses breed diversity, heterosis effects, complementarity, and advantages and disadvantages of various crossbreeding systems. Practical aspects of crossbreeding are discussed to provide guidelines for sheep producers.
Technical Abstract: The sheep industry needs to produce uniform, nutritious, lean lamb that satisfies the eating preferences of consumers. It also must improve reproductive efficiency and reduce labor requirements so that seedstock and commercial flocks are both practical and profitable under a range of production environments. Breed diversity is an invaluable resource to address these challenges. Breeds can be classified as general purpose breeds, specialized dam breeds, and specialized sire breeds based on roles in crossbreeding systems. Crossbred sheep have increased heterozygosity which is the basis for heterosis. Effects of lamb and ewe heterosis greatly impact productivity of crossbred sheep. Mating of ewes of specialized dam breeds to rams of specialized sire breeds allows favorable traits of breeds to be realized while minimizing less desirable traits (complementarity). Purebred, first-cross, rotation, and composite ewes can be used in general purpose and terminal crossbreeding systems. These crossbreeding systems vary in degree of managerial complexity and use of lamb heterosis, ewe heterosis, and complementarity. Crossbreeding exploits these genetic effects and significantly increases productivity relative to purebred flocks. Efficiency of meat production is maximized in terminal crossbreeding systems by use of specialized sire breeds to complement characteristics of crossbred ewes. It is essential to select breeds and determine breed composition so that crossbred ewes achieve the targeted lambing rate appropriate for a given production system. Crossbred rams are often useful to sire replacement ewes of optimal breed composition. These crossbred replacement ewes of optimal breed composition can generally be produced by use of first-cross, rotation, or composite programs. There are opportunities to improve communication, cooperation, and integration among producers to wisely use breed diversity and improve the genetic structure of the sheep industry.